Electrical signaling system



Mayllz, 1936. 'EA-ms' 2,040,221

ELECTRICAL SIGNALING SYSTEM Filed Jan. `4, 1953 INVENTOR WVEST 7522298TT'ORN Patented May 12, 1936 UNITED STATES PATENT OFFICE ELECTRICALSIGNALING SYSTEM Application January 4, 1933, Serial No. 650,090

3 Claims.

My present invention relates broadly to electrical signaling, andparticularly to improved procedure for receiving and utilizing theeffects in so-called carrier or modulated signal bearing currents oroscillations generally utilized in the practices of radio telephony,carrier current telephony and equivalent or like forms of electricalcommunication.

In the practice of radio telephony, for example, a definite suitablyhigh frequency for the fundamental operating or so-called carriercurrent is usually chosen or assigned for each channel or service, andalternating current of this denite frequency is continuously generatedduring active operation by the alternating current generating apparatuslocated at the transmitting terminal of the system. Separate alternatingcurrents of the sound producing frequencies of telephony are generatedand impressed upon the continuously generated carrier currents, creatingby so-called beating or interference action With the carrier current aseries or band of oscillations of frequencies above and below thecarrier current frequency in accordance with the differences between thecarrier current frequency and the various frequencies of the impressedsound representing currents.

These beat produced oscillations are generally termed the upper andlower side bands. The result is that the energy emissions emanating fromthe usual radio telephone transmitter are not wholly of the form ofcarrier current frequency oscillations varied in amplitude in responseto the impressed sound currents, but int clude a series of oscillationsof frequenciesboth higher and lower than the frequency of the carriercurrent, and differ in frequency from the carrier current frequency byan amount equal to the frequency of the sound producing current actingwith the carrier current to form the particular side band oscillation.

It is apparent that these side band oscillations, once created, can,like any other electrical oscillation, be combined with oscillations toproduce beat oscillations or currents. Obviously, if the oscillationcombined with the side band oscillation is of the same frequency as theoriginal carrier current, the resulting beat oscillations will have thesound producing frequencies of the original soundrepresentingoscillations impressed on the original carrier oscillation.In other Words, if the side band including emissions radiated by a radiotelephone or like transmitter be collected 4or received in any manner,the original sound ,producing frequency oscillations can bereestablished from these side band oscillations by impressing on thereceived energy an oscillation of the same frequency as the originalcarrier current frequency. I have found that I can advantageouslymakeuse of the above outlined pro- (Cl. Z50- 20) cedure and functioning inthe reception of radio telephone and like electrical signal eects.

The extensive use made of electrical signaling compels intensive use ofthe principles of electrical tuning or syntony for distinguishing theoperations of different communication channels one from theV other. The,principles involved in selectively distinguishing electrical signaloperations of dierent channels at different frequencies, and thepractices forv accomplishment of the results, are so well understood anddeveloped that legal supervision over such operations has long fixed andimposed severe selectivity requirements in such operations.

One common practice for satisfying the selectivity requirements is toreceive the incoming signal bearing energy on, or pass it through, oneor more highly selective (low decrement) receiving circuits. In otherwords, to depend upon resonant or accentuated resonant reception, the iftelephone broadcasting system now functioning o in the United States arespaced not less than 10 kilocycles apart in assigned operatingfrequencies. This restriction makes it necessary for the radio broadcastreceiver producers furnishing the public with broadcast receivers todesign receivers capable of reasonable selective discrimination to avoidthe objectionable effects ofthe signals of an unwanted stationoverlapping and interfering with the signals of a wanted station.

Attempt has been made to meet these severe requirements in practice bydesigning receiving circuits with lowest possible decrements, andcascading a number of suchcircuits to multiply the selectivity effects,radio receivers having three and four very low decrement tunablereceiving or input circuits in cascade not being uncommon.

This accentuation of selectivity clearly operates against faithfulreproduction of the incoming signal bearing energy. Obviously, the morethe electrical selectivity is increased, the more the energy in the sidebands is attenuated in comparison to the energy of the carrier currentper se. It is readily appreciated that with a very high order ofselectivity in the input receiving system, the energy of a side band 10kilocycles (a desirable sound producing frequency) away from the'carrier current accepted by the highly selective receiving system maybe so small compared to the carrier current energy as to have nocomparative practical Value in the sound reproductive ability of thesystem.

Summarizing these considerations, it is seen thatY faithfulness ofreproduction of the sounds represented in and carried by the side bandoscillations suffers the more the electrical selectivity of thereceiving circuits is accentuated to increase selectivity of onetransmitting station from another. Consideration of the ordinaryreceiving resonance curve clearly shows that the rate of attenuationthroughout the usual sound side band range is far from uniform.

It is one of the principal features of my present invention that I avoidserious discrimination against the effective reception of the veryimportant sound representing energies of the side band oscillations,this while providing for effective discrimination in the reception ofthe energies emanating from different transmitting stations closelyspaced in their operating frequencies. In other words, I provide formaintaining high quality of reproduction without sacrificing desirablestation-to-station discrimination.

The features of my invention and the uses of them are described inconnection With the figures of the accompanying drawing. Fig. 1diagrammatically illustrates an arrangement in which certain featuresand effects involved in my invention may be made manifest, and Fig. 2diagrammatically illustrates the adaptation of certain features of myinvention to a radio receiver.

Referring to Fig. 1, I show two three-electrode vacuum tubes V and V',conventionally energized by batteries or other suitable potentialsources GB, FB and PB, these tubes being connected in parallel relation.Transformers T1 and T2, connected to non-indicated sources of electricaloscillations, provide means for energizing the input or grid electrodesG and G through the parallel connected input circuits coupled in withthe two input transformers Ti and T2. The input oscillations introducedthrough transformer T1 divide so as to impress opposite polaritypotentials on grids G and G of the two tubes, while the inputoscillations introduced through transformer T2 divide so as to impresson the grids of the two tubes potentials of like polarity.

The output oscillations, resulting from the input oscillations,circulate in both branches of the paralleled output circuits shownconnected to anodes P and P' of the two tubes, passing in oppositedirections through the upper and lower halves of the primary winding ofoutput transformer T3. With the arrangement shown in Fig. 1, I find thatthe introduction of the usual modulated or side band bearing signalcurrents of radio telephony and the like, either separately througheither transformer T1 or transformer T2, results in little or nomanifestation of the presence of sound or audio frequency currentcomponents in the output from output transformer T3. In other Words,ordinary detection of the modulation extraction action is minor ineffect irrespective of the choice of path of introduction of theincoming signal energy.

I nd, however, that if introduction of signal bearing currents througheither path is accompanied by introduction through the other path ofoscillations of fixed frequency the same as the carrier currentfrequency from which the introduced signal bearing currents weregenerated, and of a phase other than with respect to the originalcarrier current phase (preferably the same phase or 180 out of phase),that the sound or other signal representing components of the incomingsignal ciurents become prominently inanifested in the output side oftransformer T3.

For example, if usual radio telephone signal currents extracted fromspace are introduced into the system of Fig. l through transformer T1they Will not be well heard in a listening device Corinected with theoutput of transformer T3 unless acted upon by oscillations of the samefrequency as that of the generated current out of which the incomingVsignal bearing currents were developed, and differing in phase bysomething other than 90, this accessory current being introduced throughtransformer T2.

It is immaterial whether this accessory current is originated in aseparate source, such as a local generator, or is extracted from thecarrier current component of the incoming signal current being operatedupon Iby the accessory current. It is essential only that the phase ofthe accessory current differ from the phase of the carrier current ofthe incoming signal currents by something different from 90. If theaccessory current is extracted from the received incoming signalcurrent, it is desirable that the extraction be highly selective so thatthe accessory current is substantially pure; that is reasonably devoidof side band and other adulterating energy effects.

It is apparent that if a 10W order of selectivity (broad tuning) isutilized in extracting the signal current energy from space andtransferring it from o-ne portion of the system to another prior tocombination with the accessory current, the high frequency side bandenergy is much more effectively preserved along with the low frequencyside band energy than is possible with the high order of selectivity ofreception now in general use in connection with radio telephone and likepractices.

For example, the selectivity of reception usual to present practice,comparatively considered, enormously eliminates the energy in a 500cycle sound representing side band as compared to a cycle soundrepresenting side band, both of which are of substantial importance tothe range necessary to faithful sound reproduction.

The procedure outlined by me permits of broad, non-selective receptionof the incoming signal oscillations, thereby more effectively includingthe high frequency side band components in comparison with existingreception practice, and distinguishing or bringing out the signalfrequency components by selective beating or heterodyning the stronglymaintained side band oscillations with an oscillation of frequencyessential to reconverting the side band energy to its original soundrepresenting character.

In Fig. 2, I show an arrangement for making most effective use of theprocedure I have above generally outlined in connection with usual radiotelephone reception, such as broadcast reception. A space energycollector or antenna I is coupled through a transformer 2 to a tunablecircuit 3 including a tuning condenser 4, the terminals of whichcondenser are connected to grid electrode I0 and lament 9 of athree-electrode vacuum tube 8 having its electrodes energized bypotential sources "I, I2 and I3, which potential sources areconventionally indicated as batteries.

The tunable circuit 3 is preferably made no more selective thannecessary to reasonably distinguish by resonance the desired signaltransmissions from those of its nearest in frequency assignedneighboring station. For example, in broadcast reception stations soclosely spaced geographically as to be capable of serious interferencebetween their transmissions within their respective listening areas arespaced not less than 10,000 cycles in assigned operating frequencies inthe broadcast practice in the United States, and this close spacing infrequency is confined to those stations widely separated geographically.In other words, the arrangement and practice makes it possible not toemploy an undesirable high order of selectivity in tunable receivingcircuit 3 to obtain a satisfactory degree of distinction in receivedenergies within the requirements of my procedure.

Continuing consideration of Fig. 2, the broadly received signaloscillations are combined with fixed frequency locally generatedoscillations from a suitable source, such as the indicated oscillationgenerator 6 coupled by transformer 5 with the input system. Thisarrangement results in producing a beat frequency set of oscillationsincluding the sound representing side band components in the outputcircuit of tube 8, transferable onward through the transformer I4. Thecarrier or average frequency of this beat current is represented by thedifference between the frequency of the locally generated oscillationsof generator 6 and the frequency of the carrier component of the pickedup or incoming signal bearing oscillation. In other words, the receivedsignal bearing oscillations are converted into some desired newfrequency carrier still having the same signal bearing effects.

These new frequency oscillations are passed on through split transformerII, after amplification in an indicated intervening amplifier unit I6,if desired, to a parallel connected pair of electron tubes ZI and 22similarly as described in connection with the arrangement of Fig. 1. Theoutput electrodes 30 and 3| of these parallel connected tubes, like Fig.1, are connected to the opposite terminals of the split primary ofoutput transformer 33.

In order to make effective the sound representing side band effects inthe new frequency oscillations passed along to the paralleled tubesystem above outlined, some of the new frequency oscillation energy isutilized as the accessory oscillation that must be impressed on thesignal current to bring out the effects in the manner described inconnection with Fig. 1. Coil 35 is Vshown coupled to the secondarywinding of transformer I4, and with the aid of tuning condenser 36 thisabsorbing circuit may be highly selective of the carrier or averagefrequency component of the new frequency oscillations.

This selectively absorbed accessory oscillation may, if desired, beamplified by passing through an indicated amplifier 3l, this in order toduplicate any amplification that may be imparted to the new signaloscillations by amplifier I6 previously referred to. The accessoryoscillation is shown subjected to a highly selective as to frequencyelectrical filter 38 such, for example, as the quartz crystal nowcommonly used to forcedly determine oscillating periods of electricalsystems, or other electromechanical resonance arrangements such as ispossible with magnetostriction effects.

The resulting sharply defined accessory oscillation is now impressed onthe new signal oscillations by applying the potentials developed by theaccessory oscillation in resistance 39 in shunt to filter 38 to theauxiliary grid electrodes 28 and 29 in tubes 2| and 22, whicharrangement is a preferred form of combining or bringing together thedesired effect producing oscillations over that shown in the simplethree-electrode tube of Fig. 1. While the functioning in botharrangements is equivalent in results, the auxiliary grid arrangement ofFig. 2 is the more efficient and lessens difficulties in selection ofimpedance and the like in satisfying design requirements.

'Ihe potential sources 20, 25, 32 and 40, conventionally indicated asbatteries, provide for the usual operative energizing of the variouselectrodes of tubes 2| and 22.

The arrangement provides for satisfactory phase relation between the newsignal oscillations and the accessory infiuencing oscillation. While thetransfer of energy from the secondary winding of transformer I4 to coil35 involves a phase displacement of approximately 90, the undesiredphase relation, the quartz crystal filter unit also introduces a phasedisplacement of approximately 90, so that the over all result in thetravel of the accessory current effects to the auxiliary grid electrodesof the tubes is considerably removed from the unwanted 90 displacement.

Reduction of the procedure to the fixed, one frequency basis providedfor in the arrangement of Fig. 2 is of decided benefit and advantage topractice. Other than the simple adjustment needed to select out of theantenna the energy of the desired transmitting station, the system is offixed, permanent nature throughout, and yet capable of reception at allthe frequencies of the broadcast range.

Having fully described my invention I claim:

1. In combination, a receiver of a modulated carrier having asufliciently broad tuning characteristic to amplify substantiallyuniformly the audio-frequency side bands of said carrier, means forselecting the carrier frequency from the modulated carrier including acircuit selective to the carrier frequency only, a circuit resonant atcarrier frequency and adapted to suppress all sideband frequencies, thelatter circuit being connected to said selector circuit, and a combiningcircuit including two translating devices and circuit connectionstherefor for impressing the amplified modulated carrier upon saiddevices in opposite sense and impressing the carrier from said resonantcircuit upon the devices in the same sense.

2. In combination, a receiver of a modulated carrier having asufficiently broad tuning characteristic to provide substantiallyuniform amplication of the audio-frequency side bands of said carrier, atuned circuit loosely coupled to said receiver, said circuit beingselective to the carrier frequency only, an electro-mechanical filterconnected to said tuned circuit, said filter being resonant to thecarrier frequency only, and a combining circuit including twotranslating devices and circuit connections therefor for impressing theoutput of said filter upon said devices in the same sense and impressingthe amplified modulated carrier upon said devices in opposite sense.

3. In combination, a receiver of a modulated carrier having asufficiently broad tuning characteristic to provide substantiallyuniform amplification of the audio-frequency side bands of said carrier,a tuned circuit loosely coupled to said receiver, said circuitbeingselective to the carrier frequency only, an amplifying circuitresonant at the same frequency and connected to said tuned circuit, theover-all amplification of said broad and selective circuits being of thesame order of magnitude, and a combining circuit adapted to demodulatethe broadly tuned modulated carrier by means of the output of saidresonant amplifying circuit.

ERNEST A. TUBBS.

